The present invention relates to an endless belt used in combination particularly with the pulleys of a belt drive continuously-variable speed automatic transmission.
Rubber V-belts have conventionally been used as power transmission endless belts which are used in combination particularly with the pair of pulleys of a belt drive continuously-variable speed automatic transmission to transmit torque from one to the other of the pair of pulleys, however, an endless belt formed by successively binding a plurality of plate-shaped metal blocks having the shape of the cross section of said V-belt with metal bands has become used in recent years when the power transmission belt is required of durability and high-torque transmitting performance.
An endless belt of this type is disclosed in Japanese Laid-Open Gazette for Pat. No. Sho 54-52253, wherein each of the metal blocks has a front shape which is the same with the cross section of the V-belt, that is, each metal block is formed in a trapezoidal plate having opposite side edges inclined so as to reduce the width of the trapezoidal plate along a direction from the outside toward the inside of the endless belt to form side edges to be brought in contact with the conical contact surface of the pulleys and having a thickness of around 1/4 to 1/10 of the maximum width thereof, and recesses are formed in the opposite side edges at a position displaced outward of practically the middle position between the top (outside) edge and the bottom (inside) edge thereof to form metal band supporting surfaces, a plurality of such metal blocks are arranged side by side along the direction of the thickness thereof and are bound successively by means of metal bands by engaging the metal bands with the respective recesses of the metal blocks and part of the front and back sides of each metal block between the metal band supporting surfaces and the bottom edge are tapered toward the bottom edge to allow the arcuate bending of the endless belt around the center of the rotary shaft of the corresponding pulleys.
Such a belt of this type is less liable to wear or deteriorate during the extended period of use and is suitable for transmitting a high torque, particularly for transmitting power in a continuously-variable speed transmission in which each of the pair of pulleys consists of a pair of conical flanges resiliently pressed together by the agency of a spring force, one of the pair of pulleys is adapted so that the distance between the flanges can be changed by the agency of centrifugal force and a V-belt is extended between the pulleys. However, since above-mentioned conventional endless belt is formed by arranging a plurality of metal blocks side by side and by merely engaging metal bands in the recesses formed in the metal blocks, there is a possibility of the metal blocks come off the metal bands in extending the endless belt between the pulleys after assembling the endless belt or of side slip between the metal blocks and the metal bands during power transmitting operation due to difference in the accuracy of the metal blocks or the metal bands or in the frictional force working between the inclined contact surfaces of the metal blocks and the frictional contact surfaces of the pulleys between the right side and the left side of the power transmitting assembly to cause the partial wear or partial fatigue of the metal blocks and the pulleys resulting in the deterioration of the power transmission efficiency and, in the worst case, there is a possibility of the metal blocks come off the metal bands during operation.
Furthermore, since the metal bands are engaged merely with the respective recesses of the metal blocks and do not serve to transmit a driving force from one to the other pulley, while the driving force is transmitted from the contact surfaces of the driving pulley to the metal blocks which are in engagement with the driving pulley, then from the metal blocks which are in engagement with the driving pulley to the preceding metal blocks bound by the metal bands by the pushing action of the succeeding metal blocks, then to the metal blocks which are in engagement with the contact surfaces of the driven pulley, and then to the driven pulley. Therefore, such a conventional endless belt has a disadvantage that noises are generated due to the mutual collision of the metal blocks.
Furthermore, in another endless belt disclosed in Japanese Laid-Open Gazette for Pat. No. Sho 56-52647, adjacent metal blocks are connected by thin link plates. In such an endless belt, all the load applied to the endless belt is distributed to all the link plates, therefore, the power transmission capacity of the endless belt is limited by the number of the component link plates and the durability of the endless belt is deteriorated by the concentrated load applied to the junction between the metal blocks and the link plates.